Basic question

[Dan Higdon]

Ok, time for a surprisingly rookie question.
I've seen this term before.  What EXACTLY does it mean:

"Ground Plane"

How do I make one in a circuit?  Is it the thick border of copper you
are supposed to leave around a pcb which you hook to ground and make
all of your "internal" grounds go to?
(Are you supposed to completely surround the board, or leave a gap?
I've seen both.)

Thanks,
Dan Higdon (hdan at charybdis.com)